Nitrogen Engineered Carbon Paramagnetic Centers for Spin-Mediated Photocatalysis

Defective carbon-based photocatalysts provide a metal-free platform for solar-to-chemical energy conversion. However, the fundamental role of local spin states in governing the photocatalytic activity remains insufficiently understood. Here, we report that introducing nitrogen atoms adjacent to carbon paramagnetic centers in triazine-based nanosheets enables the precise modulation of intrinsic spin properties. Pulsed electron paramagnetic resonance and first-principles calculations reveal that nitrogen incorporation increases the fraction of σ-type spin species and enhances spin-up polarization at defect sites, thereby promoting carrier separation via parallel spin alignment. Consequently, the triazine-based spin catalyst exhibits excellent performance in both cationic radical [4 + 2] cycloaddition and energy conversion applications, achieving 99% conversion with 96% selectivity and activities for hydrogen peroxide formation (17.5 mmol g^-1 h^-1), oxygen evolution (3.64 mmol g^-1 h^-1), and hydrogen production (2.41 mmol g^-1 h^-1). This work establishes spin-state engineering via heteroatom proximity as an effective strategy for activating carbon-based materials, opening avenues for the rational design of spin-directed metal-free photocatalysts.